1. Field of the Invention
The present invention relates to a lens barrel having a lens group which can be collapsed for storing and extended to a predetermined position for photographing, especially a lens barrel suitable for a zoom lens which can change a focal length by moving relatively a plurality of lens groups; and a camera equipped with the lens barrel.
2. Description of the Related Art
High performance and miniaturization are increasingly required for a photographing lens used in a photographing apparatus, such as a digital camera. In addition, a zoom lens which can change its focal length successively and has a high magnifying power is desired. These requirements are technologically challenging.
In order to cope with this technological challenge, a collapsible photographing lens, which can be collapsed to store in a main body of a photographing apparatus when not in use for photographing, is often used as an effective solution; and accordingly, a camera equipped with the collapsible photographing lens is increasing used.
Furthermore, besides miniaturization, a low-profile is also demanded. Therefore, it is required that a profile size of a lens body in a collapsed state after the lens barrel is collapsed and stored in a main body of a photographing apparatus be reduced as small as possible.
As a technological solution to cope with the low-profile demand, there has been disclosed in Japan Patent Laid-Open No. 2003-315861A (Patent document 1) and Japan Patent Laid-Open No. 2003-149723A (Patent document 2) a lens barrel which can be collapsed to be stored in a main body of a photographing apparatus and at least one of a plurality of lens groups is retracted away from an optical axis when the lens barrel is collapsed. According to the lens barrel disclosed in Patent documents 1 and 2, since the at least one of a plurality of lens groups is retracted away from the optical axis when the lens barrel is collapsed, a relatively longer retraction distance is available for the other lens groups. Therefore, it is possible to reduce the profile size in the optical axis direction of the entire lens body and accordingly the profile size of the photographing apparatus.
However, according to the configuration of the lens barrel disclosed in Patent documents 1 and 2, the lens group retracted away from the optical axis when the lens barrel is collapsed is substantially at a position located on an inner side of the maximum outer diameter of the lens barrel. Accordingly, though the profile size in the collapsed state may be reduced, the outer diameter has to be increased; that is to say, the size of the lens barrel, particularly the size of the lens barrel in a plane perpendicular to the optical axis is increased. As a result, this brings about a problem in that the size, especially the front view size, of the photographing apparatus is increased.
Furthermore, according to the configuration of the lens barrel disclosed in Patent documents 1 and 2, the lens group is retracted away from the optical axis when the lens barrel is collapsed in one moving frame or fixing member to a direction perpendicular to the optical axis. Thus there is a problem in that it is impossible for the retractable lens group to have a large moving distance along the optical axis; and there is also a limit on reduction of the profile size of the lens barrel along the optical axis when it is collapsed, and thus the profile size of the photographing apparatus.
As a technological solution to cope with the demand for a low-profile collapsible lens barrel and a camera using the collapsible lens barrel therein, Japan Patent Publication No. 3762653 (Patent document 3) discloses a guide cylinder for guiding at least one group of a plurality of lens groups to move forward or backward along the optical axis wherein the guide cylinder is made from plastic. Since the guide cylinder is made from plastic, it can be made with a complex form and this provides a possibility to increase a guiding length along the optical axis; and therefore, a moving distance along the optical axis may be increased, and as a result the lens barrel and the photographing apparatus may be made with a low-profile.
A collapsible lens barrel having a metal guide cylinder for guiding a lens-retaining frame to move forward or backward along the optical axis is also disclosed in Japan Patent Laid-Open No. 2004-233926A (Patent document 4). Although a guiding length for the lens-retaining frame is decreased since the guide cylinder is made from metal, it is possible to make a flange portion of the guide cylinder thinner; and thus it is an aim of the invention disclosed by Patent document 4 to make the lens barrel and the photographing apparatus have a low-profile when collapsed.
However, although the lens barrel disclosed in Patent document 3 may provide sufficient guiding length for the lens-retaining frame, the flange portion has to made thicker relatively since the guide cylinder is made from plastic; and this becomes a major hindrance to the low-profile of the lens barrel. Also for the lens barrel disclosed in Patent document 4, it is impossible to increase the guiding length for the lens-retaining frame since the guide cylinder is made from metal and thus there is a limit to an extending length for the lens-retaining frame when being transferred to a photographing state, in other words a movable amount from a determined extension position to the collapsed state is limited; and this eventually becomes another major hindrance to the low-profile of the lens barrel.